This is a task to improve the determination of the TransactionCoordnatorBuilder to use when one is not explicitly defined.

The series of if-checks done in EntityManagerFactoryBuilderImpl#applyJdbcConnectionProperties ought to contribute to that determination:

1. if javax.persistence.jtaDataSource is specified, assume the JTA TransactionCoordnatorBuilder
2. else, assume the non-JTA TransactionCoordnatorBuilder

So potentially have EntityManagerFactoryBuilderImpl#applyJdbcConnectionProperties return the Class<? extends TransactionCoordnatorBuilder>> to use implicitly, which we can pass along to EntityManagerFactoryBuilderImpl#applyTransactionProperties